A railway freight car generally includes a car body, a bogie, a brake device, a coupler and draft gear and other components. The bogie functions to support the car body, to guide the car to travel along a track and to withstand various loads from the car body and lines. The most common bogie of the railway freight car is a two-axle cast steel three-piece bogie including a bolster, two side frames, two wheelsets, a spring damping device, a brake device and so on.
The most commonly used damper for the bogie of the freight car is a friction damper, which includes a wedge, a damping spring and other parts. The damper is arranged in a space enclosed by the side frame and the bolster. The friction damper converts, by the effect of the angle of the wedge, a vertical support force of the spring into a horizontal side pressure of the wedge against a side frame upright column. The side frame upright column is fitted with a wear plate at a position opposite to the wedge, and a friction exists between the wedge and the wear plate. As the car body vibrates up and down, the bolster also vibrates up and down to drive the wedge to move up and down and thus cause the wedge and the wear plate to rub each other, thereby generating a friction force, that is, a damping force.
The friction damper may be classified into a constant friction damper and a variable friction damper, where the damping force of the constant friction damper is a constant and does not change with the change of a loading force, and thus it is impossible to achieve that a relative friction coefficient is within an ideal value range in both an unloaded condition and a loaded condition, and it is impossible to take into account both the unloaded condition and the loaded condition, therefore the car has a poor vertical dynamics performance.
The variable friction damper includes a wedge, a constant friction damping spring, a variable friction damping spring, an ejector rod and so on. A bottom plate under a wedge groove of the bolster has a hole. The ejector rod has an upper portion located inside the constant friction damping spring which is located in the wedge, and has a lower portion passing through the hole of the wedge groove of the bolster to be in contact with the variable friction damping spring. In the unloaded condition, the damping force is only provided by the constant friction damping spring. In the loaded condition, an inner top portion of the wedge is in contact with an upper end of the ejector rod and thus the wedge may compress the variable friction damping spring downward, therefore the damping force is provided by the constant friction damping spring and the variable friction damping spring together. Therefore, the relative friction coefficient can be within the ideal value range both in the unloaded condition and in the loaded condition, and both the unloaded condition and the loaded condition can be taken into account, and thus the car has a better vertical dynamics performance.
However, this kind of variable friction damper still has disadvantages. Specifically, since the constant friction damping spring and the ejector rod must be aligned with an axis of a variable friction damping inner spring, positions of the constant friction damping spring and which results in that the wedge have to be close to a center line of the bolster and thus a structural part between two wedge grooves of the bolster becomes smaller in size, which reduces strength of the bolster, thereby adversely affecting a service performance of the bogie.
Therefore, it is a technical issue to be addressed by the person skilled in the art to further improve the strength of a wedge groove part of the bolster so as to improve the service performance of the bogie.